Nonaqueous ink



United States Patent 3,486,912 NONAQUEOUS INK John J. Dyson, Janesville, Wis., assignor to The Parker Pen Company, Janesville, Wis., a corporation of Wisconsin No Drawing. Filed Oct. 22, 1965, Ser. No. 502,288 Int. Cl. C09d 11/16 U.S. Cl. 106-22 7 Claims ABSTRACT OF THE DISCLOSURE Low viscosity, nonaqueous, writing inks are formulated by adding a conventional coloring agent to a liquid vehicle consisting of a nonaqueous molecular associated liquid. Inks designed for use with nib-type pens as well as felt and wick writers and having a viscosity not in excess of 1000 cps, are rapid-drying, nonevaporating and nonpenetrating.

The present invention relates to nonaqueous inks and more particularly to instant drying, nonevaporating inks of low viscosity.

In the past, it has been common practice to employ water as the vehicle in most inks. A water soluble dye or dispersible pigment is placed into the water vehicle to provide the desired color. These inks have proven to be quite useful, however they are subject to the serious drawback in that they dry rapidly on the nib of a conventional pen, or in the pores of a felt writer, tending to plug the writing tip and to prevent further passage of ink.

In order to improve on the aqueous inks, heretofore attempts have been made to substitute organic vehicles for the water vehicle. Organic vehicles selected generally have shown good drying properties, that is, they did not dry so rapidly that plugging of the pens resulted. However, with few exceptions they have exhibited one very undesirable property. Organic vehicles which have heretofore been used have exhibited too high a paper penetrating ability causing staining and strike-through onto the back of the web.

It is, therefore, an object of the present invention to provide a new and improved nonaqueous ink system in which the disadvantageous limitations of the prior art are substantially obviated.

Inks of the present invention are designed to be used with nib-type pens as well as felt and wick writers. They are substantially instant drying, nonevaporating, nonpenetrating, of high surface tension and of low viscosity.

In order to produce a good, non-aquous ink, it is necessary to control three properties of the ink solution. These three properties or controls are the paper penetrating ability of the ink, the rate at which the ink leaves the point of the pen, and the drying rate of the ink.

The three solution properties can all be controlled individually without any great difficulty. The problem arises in preparing a single nonaqueous ink composition in which all three properties are controlled.

The paper penetrating ability of ink is dependent on both the solution properties of the ink and on the design of the pen delivering the ink to the web. If too much ink leaves the point of a pen while writing, then drying time is prolonged and the ink tends to be drawn into the capillaries of the web causing undesirable strike-through and feathering of the written character.

The most desirable writing condition is flat-line delivery, that is, the cross section of the ink line leaving the point is flat rather than hemispherical. A flat line has good drying properties since it contains a minimum of Patented Dec. 30, 1969 volume of ink and therefore also gives maximum length of line per gram of ink. The physical characteristics of the nib and felt writer tip should be determined so that a fiat or starved ink line is delivered to the web. If the properties of the pen are controlled, then the only remaining variable is the ink solution itself.

Paper upon which writing or printing is to be made is usually coated with a sizing that may include a base sizing of rosin and a surface sizing of a material such as starch. The starch sizing molecules are held on the surface of the paper by the base sizing of rosin molecules that have a tendency to orient themselves to the base web fibers and to align themselves closely together normal to the coated surface. This rosin size obstructs the water of the starch size from penetrating to the web, while the starch surface size provides the dominant effect for ink control. The starch molecules do not align themselves as do the rosin molecules, but, rather, the starch molecules lie at random and act to prevent ink feathering by limiting the spaces through which the ink vehicle molecules can penetrate to the web, and in addition to this physical effect, by chemically adsorbing the vehicle molecules at the numerous hydroxyl sites. Thus starch increases the sizing efficiency by providing both a physical and a chemical exclusion, while still providing a passageway for ink to penetrate the web sutficiently for good drying rates based on limited absorption into the paper web. The problem with organic ink systems is now believed to be due to the fact that most organic vehicle molecules are small enough to penetrate between the oriented starch molecules so that they reach the base web and cause feathering.

It has now been found that molecular associated liquids are a superior nonaqueous vehicle for use in a low viscosity ink which is to be used in conventional nib-type pens as well as felt or wick writers. As a result of this discovery, it is now possible to design an entirely new class of low viscosity, i.e., not in excess of cps., ink systems having tailor-made physical properties in accordance with intended use.

Broadly, the present invention provides an instant drying, nonevaporating, low viscosity ink comprising a major proportion of a nonaqueous liquid vehicle selected from the class consisting of (i) a substance exhibiting intramolecular association in the liquid state through hydrogen bonding between different molecules of the same substance, and mixtures of such substances, (ii) a solution of a substance containing at least one hydrogen bonding site per molecule, dissolved in a solvent which is itself capable of hydrogen bond formation by intermolecular association between solvent and solute molecules, and (iii) mixtures of (i) and (ii), and a minor proportion of a coloring agent, present in an amount at least sufficient to provide a minimumly acceptable coloration for marking purposes when used with a writing instrument.

As used herein, a molecular associated liquid is one comprising molecules in which an atom of hydrogen is attracted by rather strong forces to two atoms, instead of only one, so that it may be considered to be acting as a bond between them. This hydrogen bond is largely electric in character and can form only between the most electronegative atoms. Its existence is generally established by conventional spectroscopic and crystal-structure studies and by the analysis of physico-chemical data. Fluorine, oxygen and nitrogen all form strong hydrogen bonds, the strength of the bond increasing as the electronegativity of the atoms, which are bridged by hydrogen, increases. For example, the phenols form stronger hydrogen bonds than aliphatic alcohols because of the increase in electronegativity of the oxygen atom resulting from resonance. Examples of hydrogen bonds existing in molecular associated liquids are given below:

OH...O NH...N NH...F NH...O

In certain instances, where the carbon atom is attached to a strongly electronegative group, hydrogen bonds are formed between carbon and oxygen (C-H O) and between carbon and nitrogen C-H N). Similarly, chlorine and sulfur can form weak hydrogen bonds if the other atoms are strongly electronegative, e.g., OH...ClandN-H...S.

Accordingly, molecular associated liquids are those which contain relatively complex molecular species formed by the linking together of a relatively large, but indefinite, number of single molecules by hydrogen bonds. In substances which are intramolecularily associated the hydrogen bond is between two similar atoms derived from different molecules of the same substance, as in the case of the alcohols, or the bond is between two dissimilar atoms derived from different molecules of the same substance as in the case of formamide. On the other hand, intermolecular association refers to the formation of molecular compounds between two substances by hydrogen bonding in the liquid state, for example, when a hydroxylic compound is mixed with another similar compound, or with an ether, ester, ketone or the like.

Preferably, the organic vehicle chosen will be a small molecule which exhibits dior poly-functional hydrogen bonding to the extent that even in the liquid state it appears to have quasi-crystalline properties. This hydrogen bonding causes the organic molecules to group or clump together in a three-dimensional network. The clumps of molecules are too large to penetrate between the sizing molecules on the base web and are therefore precluded from marking and penetrating the web. When such materials were tested on sized webs, they were found not to penetrate the web to any appreciable amount. On the basis of this discovery, a novel series of nonaqueous inks has now been developed.

Broadly, any of the commonly available coloring agents can be used to form a molecular associated organic ink system in accordance with the present invention. The coloring agent can be an organic dye or an inorganic pigment. Preferably, organic dyes selected for use with the nonaqueous vehicle should be soluble in both the vehicle and in water. If a water soluble dye is not used, the dye has a tendency to precipitate out of solution as the vehicle picks up moisture. The precipitated dye can cause plugging and poor start-up of the pen, thereby obviating the advantages obtained through the use of a nonaqueous vehicle.

The following representative organic dyes have been found particularly suitable in the nonaqueous ink system of the present invention. They are each soluble in water as well as in molecular associated liquids such as formamide:

National Alphazorine PG Conc. 200%, CI. 42090 National Fast Light Yellow 2 G, C.I. 18965 Victoria Pure Blue B0, C1. 42595 Brilliant Scarlet 3 R, C.I. 16255 Erie Black G.A.C. Conc., CI. 30235 Diphenyl Dark Blue R, C.I. 30205 Ink Blue PP Dye, U.S. Pat. 2,489,463

The first five of the above dyes are made by National Analine Division of The Allied Chemical and Dye Corporation, 40 Rector Street, New York, N.Y., while the 4 Diphenyl Dark Blue R dye is made by The Geigy Company, 899l Barclay Street, New York, N.Y., and the Ink Blue PP dye is as disclosed in the U.S. Patent 2,489,- 463 issued to The Parker Pen Company as assignee of William B. Reynolds.

In the new class of inks the molecular associated liquid is the principal vehicle and does not require the use of any other materials which might be termed a solvent for the ink. While various additives can be incorporated into the ink system to control the amount of paper penetration, the drying rate and surafce tension to viscosity relationship, these materials are added in minor amount sleaving the molecular associated liquid in excess of the total concentration of the additives, i.e., in excess of 50 mole fraction percent.

Approximately 35% by weight of water-soluble dye tends to be a maximum upper limit for use in the associated liquid based inks. At this composition, the ink solution generally is too viscous for use in instruments designed to dispense true fluid. It would, however, be possible to use these inks in a ball point pen. Accordingly, nonaqueous inks of the present invention comprise in the range of 9965 percent by weight of a molecular associated liquid or solution and in the range of 135 percent by weight of a coloring agent.

The draftsmans ruling pen is a practical device for determining a preferred upper limit for dye concentration. In such pens, the nib acts as its own capillary reservoir and flow problems at the upper limits of fluid ink vis- V cosities are greatly reduced because of the nibs simple nature. Using this test, approximately 1-25 percent by weight of dye appears to represent the preferred range for the associated liquid based ink. Above this composition, the ink generally is too viscous to be delivered freely from the nib.

In conventional fountain pen nibs, with the complexities of reservoir and feed systems to be faced, much lower viscosities are used. For such inks, the optimum viscosities occur at approximately 4% by weight dye and might be reduced to as low as 1% by weight in some cases. This latter value is normal for low quality, water-based inks and could serve as a minimum acceptable color limit with approximately 4% by weight optimum for nib-type pens.

An additional feature of the present invention is the discovery that additives containing at least one hydrogen bonding site per molecule advantageously can be incorporated into a molecular associated liquid-base ink to produce nonaqueous inks that are substantially nonevaporating, nonpenetrating, of high surface tension and of low viscosity. On the basis of this discovery, a novel series of nonaqueous inks was developed employing molecular associated liquids such as formamide as the principal ink vehicle.

While molecular associated liquids do not penetrate sized webs to any appreciable extent, it has now been found that the paper penetrating ability of such liquids can be decreased still further by the use of clumping agents which increase the extent of hydrogen bonding in the solution and which cause other materials with little bonding with the additive.

Organic materials containing amino, hydroxyl, and fluoride groups are suitable clumping agents. Examples are substances such as sucrose, sucrose dioleate, arabitol, guar gum, raflinose and trimethylol propane. When added to molecular associated liquids exhibiting di-functional hydrogen bonding in minor amounts, these substances were found to decrease the paper penetrating ability of the ink vehicle.

It has also been discovered that the evaporation rate or drying rate of the associated liquid based inks can be controlled further through the use of minor amounts of nonevaporating additives. Materials capable of hydrogen bond formation, such as liquid polyethylene glycol or monofluoro-halo-mono alcohols, materially reduce the evaporation of the ink vehicle.

The monofluoro-halo-mono alcohols are generally structured as follows:

Compounds of this class incorporate two hydrogen bonding sites, F and OH. These being located at the ends of the molecule tend to cause quasi crystal formations within the fluid which simulate the properties of water, especially where x is a small number. These hydrogen bonding sites also make for polarity for the purpose of dissolving dyestulfs and cause these molecules to gather around and associate with multi-hydroxyl additive agents like sucrose dioleate.

The monofluoro-halo-mono alcohols contain the property of dye solubility by virtue of their polarity adjustment so the delivery off the end of a nib would be dominated by the surface tension toward properly starved lines with flat cross sectional shapes. The halogen substitution provides heavy molecules which are hard for the thermal energy to eject into the atmosphere and volatility is thus controlled downward. Viscosity is low and the surface tension is usually higher than normal in quasi crystalline liquids. An example of a suitable nonevaporating additive is 2, 3 tetrachloro-4- monofluoro butyl alcohol.

The inmportance of nonevaporating additives results from the relationship which was found to exist between the surface tension and viscosity of the vehicle. If the surface tension is stronger than the viscosity so that the surface tension dominates the flow properties of the vehicle, less ink will be delivered from a nib to the paper during writing. It is possible then to provide an almost instantaneously drying ink which will not strike through the paper or cause feathering in view of the small amount of ink deposited in forming a line. If the fluid vehicle has a low enough viscosity, and a high enough surface tension, it will form lines as well as a water-based ink. Viscosity must be low with respect to the fluid surface tension for this control to function. Thus, at higher surface tension, higher viscosity can be tolerated. While the flow rate of a liquid from a tube will be retarded upon an increase in its viscosity, an increase in viscosity of a liquid in the form of free drop that is being spread by means ofa stylus or nib will increase the flow rate, and it therefore is only essential that the surface tension dominate the flow and be high enough to hold the fluid to the nib against the viscosity influence tending to pull the fluid off the nib.

If it becomes necessary to dilute the ink composition, for example to reduce the viscosity, it is desirable to reduce the surface tension as little as possible. Suitable nonaqueous diluents are the halogen substituted hydrocarbons in that they, for the most part, have low viscosities and can be obtained in pure form. The following are representative halogen susbtituted non-aqueous diluents: trifluoro trichloroethane, trichloroethylene, perchloroethylene, mono bromo difluoro trichloroethane and mono bromo difluoro mono iodo dichlorethane.

It is considered that the main feature to be offered by nonaqueous ink is a new convenience in writing. This goal is met by the production of essentially nonvolatile fluids which will not evaporate as quickly as water and thus dry out in pens. On the other hand, they must also dry rapidly on paper. Here again the halogen compounds have advantages. The halogen atoms are all heavy atoms. When used to replace hydrogen, they increase the weight of the new molecule. Being substantially heavier, it takes more kinetic energy to hurl them from their liquid surface into the atmosphere. In other words, they do not evaporate rapidly. On the other hand, when spread out into thin films as is the case in written lines, other chemical principles apply and because of their highly negative properties, they do evaporate somewhat more rapidly.

Hydrazine is also an excellent diluent for use in lowering the viscosity of the nonaqueous inks. However, inks prepared with hydrazine require special handling when 6 used because of the toxicity and explosion hazard involved.

However, the high surface tension of hydrazine and low viscosity would permit greater amounts to be added to the molecular associated liquid without averaging down its surface tension, and in principle it would be a preferred diluent.

To assist in the prevention of ink dry-up on the point of a pen, which can cause plugging or poor start-up, it has also been found to be desirable to add a hygroscopic agent to the ink solution. Vehicles such as formamide exhibits hygroscopicity by themselves, however this property can be enhanced by the addition of minor amounts of substances such as anhydrous lithium chloride, anhydrous calcium chloride, potassium acetate, glycerine, or the like. Through the use of these materials, the point of the pen tends to stay moist ready for instant writing even if left uncovered for a considerable length of time.

The concentration of additive or additives in the finished associated liquid-base inks is not critical. Various concentrations of clumping agents, hygroscopic agents and/ or evaporation inhibitors can be employed depending upon the properties of the ink desired and the intended use. In general, a minor but specific property improving amount of each will be utilized. Specific concentrations can vary in the range of about 1 to 34 percent by weight.

The maximum additive concentration in associated liquid-based inks would occur at fifty mole fraction percent of additive. Beyond this concentration, there would be more additive molecules than there are vehicle molecules. The practical range is, therefore, not greater than thirty-three mole fraction percent. This occurs when the additive has two hydrogen bonding sites per molecule and thus two di-functional vehicle molecules can associate with one additive molecule.

Inks prepared as described above have been found to be substantially nonevaporating, nonpenetrating, of high surface tension, of low viscosity and capable of producing sharply defined markings on a web.

As can be seen from foregoing discussion, the low viscosity inks of the present invention can be formulated from a variety of constituents. They include ink systems in which the vehicle consists of a single substance, i.e., a molecular associated liquid through di-functional or poly-functional hydrogen bonding between different molecules of the same substance. Mixtures of such substances can also be employed as vehicles forming the principal constituent of the ink.

The properties of the ink can be controlled further through the use of additives which are mono-, di-, or polyfunctional hydrogen bond formers. Mixtures of such additives can also be utilized to produced inks of high surface tension and low viscosity. By the use of such additives, it is even possible to use a mono-functional molecule having only one hydrogen bonding site for the principal ink vehicle.

Mono-functional hydrogen bonding liquids suitable for use as a vehicle in inks having a viscosity not in excess of 1000 cps., include aliphatic alcohols, e.g. methyl, ethyl, etc., simple amines, e.g. n-butyl amine, tert.-butyl amine, etc., ketones, e.g. acetone, etc., and the like. Examples of suitable di-functional liquids include hydrazine, formamide, dihydroxy alcohols, esters, diamines, symmetrical difluoro-tetrachloro ethane, and the like. Suitable polyfunctional vehicles include polyhydroxy alcohols, e.g. glycerol, trimethylol propane, etc., polyamines, e.g. triethylene, tetramine, hydrazine polymers, fluorinated hydrocarbons, e.g. trifluorotrichloro ethane, and the like.

Each of the above substances can also be used as an additive in an ink system in accordance with the present invention. Additional additives are solid and liquid substances containing amino, hydroxyl or fluoride groups which are soluble in the above ink vehicles, e.g. sucrose, sucrose dioleate, arabitol, guar gum, raflinose, trimethylol propane, and the like.

The following examples are representative of the various embodiments of the ink of he present invention:

EXAMPLE 1 An example of a basic formula comprising a dye in a formamide vehicle. The novel formamide-based inks of the present invention are prepared by first insuring that the formamide is ammonia-free, as by a moderate heating and stirring, and thereupon adding the dyestauif and in some cases other additives to form a solution. The solution is ready for use after filtering. Where convenient, the additive is dissolved in the formamide prior to addition of the dyestuff.

Grams Formamide 100 Dye (Natl, Alphazorine F.G. Conc. 200%) EXAMPLE 2 A second example of a basic formamide ink formula.

Grams Formamide 100 Dye (Diphenyl Dark Blue R) 1.30

EXAMPLE 3 An example of a formamide ink including an anhydrous deliquescent agent.

Grams Formamide 100 Dye 5 Lithium chloride (Anhydrous) 1.05

EXAMPLE 4 An example of a formamide ink including a nonevaporating additive.

Grams Formamide 100 Dye 5 Polyethylene glycol No. 200 5.52

EXAMPLE 5 A second example of a formamide ink including a nonevaporating solvent additive. Hydroxyethyl formamide is particularly desirable in that it is a heavier molecule that increases the viscosity of the solution Without materially affecting its surface tension.

Grams Formamide 100 Hydroxyethyl formamide 11.1 Dye (Ink Blue PP) 5.55

EXAMPLE 6 An example of a formamide ink including a nonevaporating additive and a deliquescent additive.

Grams Formamide 100 Dye 5 Polyethylene glycol No, 200 5.25 Lithium chloride (anhydrous) 3.15

EXAMPLE 7 An example of a formamide ink including a non-evaporating additive and a deliquescent additive that is controlled by water addition.

Grams Formamide 100 Dye 5 Polyethylene glycol No. 200 5 .25 Solution a below 3.15

(a=2 grams lithium chloride (anhydrous) in 73 grams of water) EXAMPLE 8 An example of a formamide ink that includes additional clumping molecules to aid the normally self-clumping solvent molecules of formamide and to improve their paper performance.

Grams 10.17 4.20

Formamide Arabitol (a sugar relation) Dye EXAMPLE 9 An example of a formamide ink including pure sucrose as a clumping agent. Here the sucrose is soluble in its pure, unesterified form, and acts as a clumping agent. The built-in di-functional hydrogen bonding effect of the formamide vehicle makes it a good solvent for the sucrose.

Formamide cc 17 Sucrose (pure) grams 0.57 Dye do 0.01

EXAMPLE 10 An example of a formamide ink including a. monofluoro-halo-mono alcohol as an evaporation inhibitor.

Formamide 2,3,tetrachloro-4, monofiuoro butyl alcohol 1 Ink Blue PP 0.5

EXAMPLE 11 Mole traction percent; of additive Length of line Viscosity (cps) obtained (inches) In a similar test addition of 5 mole fraction percent of raflinose to a tert. butyl amine vehicle increased the length of the ink line from 2.7 inches for the control test to over 30 inches in the case of the experimental test, showing the etfectiveness of a hydrogen bond forming additive used with a vehicle capable of being hydrogen bonded. In a comparative test, it has been shown that an ink consisting of 10 grams of tetrachloroethylene (Cl C=CCl 1.4 grams of sucrose dioleate and trace quantities to spirit sol Fast Blue R penetrates a writing paper so quickly that it is impossible to draw a Well defined line, whereas the same ink system using 10 grams of trifiuoro trichloroethane instead of the tetrachloroethylene is non-pentrating and forms a well defined line.

It is understood that the compositions presented in the above examples are in no Way limiting, the invention be ing limited only by the scope of the following claims.

What is claimed is:

1. A rapid-drying, nonevaporating, writing ink having a viscosity not in excess of 1000 c.p.s. consisting essentially of the range of from 65 to 99 weight percent of formamide and in the range of from 1 to 35 weight percent of a coloring agent present in an amount at least sufiicient to provide an acceptable coloration for marking purposes when used with a writing instrument.

2. Writing ink according to claim 1, consisting essentially of from 65 to 99 Wt. percent formamide, from 1 to 35 wt. percent of a coloring agent and from 1 to 34 wt. percent of an additive comprising a compound having at least one hydrogen bonding site per molecule selected from the group consisting of sucrose, sucrose dioleate, arabitol, guar gum, If'gtifillQSti. trimethylolproprane, polyethylene glycol, 2, 3, tetrachloro-4, monofluoro butyl alcohol, hydroxyethyl formamide, methyl alcohol, ethyl alcohol, n-butyl amine, t-butyl amine, acetone, hydrazine, difiuoro-tetrachloro ethane, glycerol, triethylene tetramine, trifluoro trichloro ethane and mixtures thereof.

3. A rapid-drying, nonevaporating, low viscosity writing ink consisting essentially of from 65 to 99 wt. percent formamide, from 1 to 35 wt. percent of a coloring agent and from 1 to 34 wt. percent polyethylene glycol.

4. A rapid-drying nonevaporating, low viscosity writing ink consisting essentially of from 65 to 99 -Wt. percent formamide, from 1 to 35 Wt. percent of a coloring agent and from 1 to 34 wt. percent hydroxyethyl formarnide.

5. A rapid-drying, nonevaporating, low viscosity Writing ink consisting essentially of from 65 to 99 wt. percent formamide, from 1 to 35 Wt. percent of a coloring agent and from 1 to 34 wt. percent sucrose.

6. A rapid-drying, nonevaporating, low viscosity Writing ink consisting essentially of from 65 to 99 Wt. percent formamide, from 1 to 35 Wt. percent of a coloring agent References Cited 2 UNITED STATES PATENTS 10/1950 Voet 106-30 2,684,909 7/1954 Leekley et al. 106-24 2,690,973 10/1954 Voet 106-20 2,966,417 12/1960 Anderson 106-22 JULIUS FROME, Primary Examiner I B. EVANS, Assistant Examiner US. Cl. X.R. 

